1. Field of the Invention
The invention pertains to rolls for treating web materials such as paper, non-woven materials and the like for compacting and elongating the same.
2. Description of the Prior Art
In certain industrial applications of paper, woven and non-woven materials which are generally provided in web form, it has been found advantageous to compact the materials so as to increase their density while simultaneously producing a soft texture and increasing their extensibility. For example, in industrial uses of paper for producing bags for packaging bulk products, the manner in which these bags are handled during shipping generally requires a material which is tough and extensible to avoid tears and the like when the bags are packed for shipment. By compacting the paper materials when it is in web form, not only is their strength and stretchability increased, but the texture is somewhat softened. In the case of web materials of woven and non-woven textile materials, compacting has been found to improve the strength, texture and extensibility in a similar manner.
Prior art devices have been developed to compact such web materials utilizing double roll compactors capable of subjecting the webs to forces within the plane of the material sufficient in magnitude and direction to compact the web within commercial specifications. Conventional double roll compactors generally include a soft rubber covered roll nipped with either a steel or cast iron roll to compact web materials passing through the nip. As will be seen in the description hereinbelow, in order to compact web materials in the plane of the web, it is necessary to provide an asymmetric displacement of an incompressible material -- such as rubber -- which forms part of a cover member of the nip roll. This material displacement results in recoil of the rubber at the nip exit, with the net velocity of the surface of the deformable cover which contacts the web material having sufficiently reduced across the nip so as to create a velocity and force differential across the nip and within the plane of the web sufficient to compact the material.
In the prior art it has been necessary to drive both the steel roll and a roll covered with rubber material at different rotational speeds to produce this asymmetric condition. A higher speed is necessary for the steel roll to force rubber to flow into the nip at the nip entrance and for the rubber to recoil at the exit portion of the nip to produce compaction of a web material therebetween. In practice, this necessary speed differential is generally achieved by the use of a generator to brake the speed of the rubber covered roll. In this way, power is recovered which -- together with additional input power -- is used to drive the steel roll. The arrangement has several inherent drawbacks, the primary disadvantages being: (1) extremely large and expensive motors, generators and electrical controls are needed to handle the power being recirculated through the compactors; (2) the compactor itself must be sufficiently substantial to accommodate this excess torque which is being recirculated; and (3) the power is lost due to the inefficiencies of the conversion. Machines of this type are generally known as "MD Compactors", the expression MD referring to the fact that the web materials move through the nip in the "Machine Direction".
U.S. Pat. No. 1,537,439 to Griffith relates to a press roll for paper making machines having a vulcanized rubber member having pores providing air cells in the circumference thereof to render the same repellent so as to express the surplus water from paper stock. U.S. Pat. No. 1,973,690 to Lade relates to a calender roll which is inherently heat resisting and possesses a body and surface of such characteristics as will adapt the roll for use in calendering machines where it is desired to operate on fabric, paper and the like. The roll comprises in combination, a shaft having a roll body thereon held in compressed relation between flanges at opposite ends thereof, the body comprising superposed sections of fibrous material including degummed fibers of ramie. U.S. Pat. No. 3,362,862 to Brundige et al relates to an apparatus for supercalendering paper comprised of a vertical stack of rolls and a frame means, the stack of rolls comprising a series of alternate hard and soft rolls mounted for rotation and held in vertical alignment and touching relationship to each other by the frame means with means provided for feeding paper to be supercalenderized into the stack of rolls and means for withdrawing the paper after it is passed through the stack. Drive means for driving the lowermost roll of the stack is provided and a substantial outer portion of the soft rolls is comprised of a polyaryl carbonate material. U.S. Pat. No. 3,447,600 to Greene relates to a construction of a roll for machinery which has a specifically elastomeric cover having an inner work region and an outer nonworking region. The inner working region is preforated by generally longitudinal spiral channels in order to counteract the inability of its elastomeric mass to compress and in order to flow a cooling liquid for temperature control. The outer nonworking region has a higher modulus of elasticity than the inner working region so as to sufficiently isolate the outer operation of the external surface of the roll from the inner operation of the conduits. U.S. Pat. No. 3,501,823 to Gregersen et al relates to a calender roll having a central core and a roll filling composed of discs fitting on the core and compressed together to form an essentially solid body, the disc being made of a polymeric sheet material having a biaxially oriented molecular structure. U.S. Pat. No. 3,753,276 to Reisch relates to a calender roll comprising a polymeric roll covered and adapted to be secured in frictional engagement with a rigid mandrel under static conditions which will permit relative movement between the roll and the cover under operating conditions.
None of these patents suggest a nip roll for treating web materials having a reinforced elastomer cover member so constructed as to uniquely provide asymmetric displacement of the incompressible elastomer material during nipped rotation so as to result in the desired treatment of web materials such as the roll which I have invented. Moreover, none of these patents suggest a roll which is capable of compacting, elongating, and shredding paper, woven and non-woven web materials and the like without the need for complex external differential drive means.